Production of oil by fluid drive



Filed Dec. 9. 1963 PRoDUcT|oN\ `mJECTloN FLUID X X 24 20 SZFREE co2 2o4o% BY cARoNATED FRESH WATER (noo-1500 PsvG) i INVENTOR. n .1. c. TRANTHAM Y Z I 2,57

ATTORNEYS This inventionrelates to a method or process for producing oil from an oil reservoir by fluid drive, utilizing. in situ generated CO3.

.The recovery of oil by fluid drive `utilizing various fluids is conventional in the petroleum production art. The utilization of liquid and gaseous carbon dioxidein the displacement of oil from porous media has been demonstrated in laboratory experiments by .Beeson and Ortlolf, Transactions of the American Institute of Mining, Metallurgical and Petroleum Engineers, 2.16, 388 (1959). In utilizing liquid CO2 the processsuiers from some of the same disadvantages as are experienced with liquid propane and liquid butane as the displacing and driving agents, viz., instability of 'the displacement front and premature breakthrough of the displacing agent. This ditliculty can be reduced or eliminated lby the generation of liquid carbon dioxide in situ so that the liquid COgbank grows in volume as it moves away from the injection well s into the formation and its tendency to become narrower is otset. l j

This invention is concerned with a method of produc mg oil from an oil reservoir utilizing CO2 produced in situ so as to eliminate the disadvantages set forth above.

Accordingly, it is an object of the invention to providean,V improved process for the uid displacement or drive of oil. A further object is to provide a process for producing oil by liuid drive utilizing CO2 as the principal displacing medium. Other objects of the invention will t become apparent from vconsideration of the accompanying disclosure.

A broad 4aspect of the invention comprises injecting alternate slugs of concentrated brine and fresh water saturated with CO3 at elevated pressure into an oil reservoir through an injection well and driving the injected slugs through the reservoir to a production weil to re,- cover oil therefrom. A convenient and eicient method comprises injecting the slugs through the center well of 4a tive, seven or nine-spot pattern and producing through the ring wells.- It is also feasible and advantageous to utilize the injection and production techniques with different well patterns disclosed in U.S. applications S.N. 129,422, led August 4, 1961, now U.S. Patent'N-o. 3,- 120,820, and S.N. of Melcon Santourian.

223,298, ined september 1o, 1962,

nitedzStatesv .aten-r1. l.

The amount of each slug injected should be in the range f of about three to ten percent of the pore volume in the i well pattern to b'e produced, and preferably about tive percent of the pore volume. The salts used in the brine may'v be sodium, 'calcium or magnesium chloride.

The i brine obtained'from well `formation is ordinarily sufciently concentrated for use in the process; however, if such is not the case, additional salt may be introduced in solution to bring the concentration within the range of 20 to 40 percent by weight.

The first slug of brine is followed by a slug of fresh water saturated with CO2 at a pressure in the range ot y 1100 to 1500 p.s.i.g. and this water-CO2 slug is then fob lowed by a second slug of brine. The alternate slugs of brine and C03-containing water are followed by injec- L at ment,.the carbondioxide-in thefreshwater slug is saltedout. Of Course, some of thesalted-out CO2 dissolves in the vbrineslug, lbut because-of the low solubility of carbon .dioxide inthe concentrated brine, a'rnajor portion of it lrernainsinsoluble and-this separate, linsoluble portion has a desirable displacing effect on the reservoir oil.

For reservoirs whose temperaturesare below .the critical temperature of COL; (88 Fi), the carbon dioxide ,forms aliquid bank at the pressures used in the process. A

(This can be lower for lower reservoir temperatures.) As the slugs move through the reservoir, thezones of miscibility at the leading and ,trailing edges (or interfaces) of the carbonated water grow and causel the two banks of liquid carbon dioxide to become larger. l'Thus the reservoir is swept 'by a system of 'slugs as illustrated in the drawing, referred to below. first carbon dioxide bank to -becomeunstable is resisted by the growthof the volume of liquid carbon dioxide and is backed up by the secondyliquid carbon dioxide bank.

In this wayvahigh efficiency sweep results. When :he

temperature is above the critical temperature of CO2, the CO2 in gaseous lphase effects 'a similar: sweep of the reservoir.` I

Theinvention is further illustrated by reference to the accompanying schematic drawing which is an elevation through a reservoir showing the injected slugs in place at a given step of the process.

Referring to the drawing a stratum or reservoir 10 isV penetrated by an injection well 12 and a production well 14. Well 12-may be a center well of a five, seven or nine-spot pattern whilewell14 may be one of the ring wells of said pattern. lt is also feasible to provide a line of injection wells 12 with aline of production wells 14 on either side of the injection wells. Numerals 16, and 18 designate saturated brine slugs with saturated carbonated fresh water slug 20 therebetween. Free carbon dioxide is shown at 22 and 24 at the leading and trailing edges or interfaces of the CO2-containing slug. It is also feasible to inject a second slug of the saturated carbonated waterv behind slug 18 and follow this with a third slug of brine. Injection iluid is indicated at 2S after it enters the reservoir through injection well 12. As the injection of driving fluid is continued, slugs 16, 1S and 20 along with the CO2 Zones of miscibility 22 and 24 are driven through the stratum 10 to production well 14 .andthe produced oil is recovered therefrom.

Reasonable variation 'and modification are possible within the scope of the foregoing disclosure, the drawing content ofthe fresh water increases during this move-.

The tendency of the.

(2) thereafter, injecting a slug of fresh water saturated with CO2 at a pressure in the range of 1100 to 1500 p.s.i.g. into said reservoir as in step (l) while maintaining the injection pressure in said range;

(3) repeating step (l) after step (2)- to provide alternate sections in the reservoir containing Ainjected brine vand water saturated with CO2, whereby CO2 is salted-out at the interfaces between the slugs; and

(4) driving the injected uids toward said production well 'so as to produce oil from said .reservoir thru said production well.

2. Thel process of claim 1 wherein step (4) is effected by injecting water thru the injection well.

3. The process-of claim l'wherein the slugs of brine and water saturated with CO2 are in the range of about 3 to l0 percent of the pore volume of the reservoir area being produced.

4. A process for producing oil from an oil'reservoir penetrated by wells in one -otf a 5, 7. and 9-spot pattern comprising the steps of:

(1) injecting a first slug of concentrated brine (20-40 weight percent salt) thru at -least one of the wel-ls in said pattern into the reservoir toward at least one production well in said pattern;

(2) following step (1), injecting a second slug of fresh water saturated with CO2 at a pressure in the range of 1100-1500 p.s.i.g. behind and adjacent said rst slug while maintaining the pressure in said range;

(3)- repeating step (1) so as to position a third slug of brine adjacent said second slug;

(4) land injecting water behind said third slug -as a driving uid so as to drive said slugs thru the reservoir toward said at least one production well;v and (5) recovering oil produced by the foregoing steps.

' References Cited bythe Examiner UNITED STATES PATENTS 2,875,833 3/1959 Manin 1664-9 -3,o65,79o :i1/1962 Holm, 16s- 1 X 3,120,870 2/1964 Santourian 166-9 2 CHARLES E. ocoNNELL, Primary Examiner.

BENJAMIN HaRsH, Examiner.

'ma Mii' 

1. A PROCESS FOR PRODUCING OIL FROM AN OIL RESERVOIR PENETRATED BY AN INJECTION WELL AND A PRODUCTION WELL, COMPRISING THE STEPS OF: (1) INJECTING A SLUG OF CONCENTRATED BRINE INTO SAID RESERVOIR THRU SAID INJECTION WELL TOWARD SAID PRODUCTION WELL; (2) THEREAFTER, INJECTING A SLUG OF FRESH WATER SATURATED WITH CO2 AT A PRESSURE IN THE RANGE OF 1100 TO 1500 P.S.I.G. INTO SAID RESERVOIR AS IN STEP (1) WHILE MAINTAINING THE INJECTION PRESSURE IN SAID RANGE; (3) REPEATING STEP (1) AFTER STEP (2) TO PROVIDE ALTERNATE SECTIONS IN THE RESERVOIR CONTAINING INJECTED BRINE AND WATER SATURATED WITH CO2, WHEREBY CO2 IS SALTED-OUT AT THE INTERFACES BETWEEN THE SLUGS; AND (4) DRIVING THE INJECTED FLUIDS TOWARD SAID PRODUCTION WELL SO AS TO PRODUCE OIL FROM SAID RESERVOIR THRU SAID PRODUCTION WELL. 